U.S. patent application number 12/921896 was filed with the patent office on 2011-03-17 for assemblies and methods for reducing warp and bow of a flexible substrate during semiconductor processing.
This patent application is currently assigned to Arizona Board of Regents, a body Corporate of the State of Arizona acting for and on the behalf of A. Invention is credited to Hanqing Jiang, Douglas Loy, Shawn O'Rourke.
Application Number | 20110064953 12/921896 |
Document ID | / |
Family ID | 41011823 |
Filed Date | 2011-03-17 |
United States Patent
Application |
20110064953 |
Kind Code |
A1 |
O'Rourke; Shawn ; et
al. |
March 17, 2011 |
Assemblies and Methods for Reducing Warp and Bow of a Flexible
Substrate During Semiconductor Processing
Abstract
Methods are described for addressing the bowing and/or warping
of flexible substrates, attached to a rigid carrier, which occurs
as a result of the thermal challenges of semiconductor processing.
In particular, viscoelastic adhesives are provided which can bond a
flexible substrate to a rigid carrier and mediate the thermal
mismatch which often is present due to the distinctly different
materials properties of most flexible substrates, such as plastic
films, with respect to rigid carriers, such as silicon wafers.
Assemblies are also provided which are produced according to the
methods described herein.
Inventors: |
O'Rourke; Shawn; (Tempe,
AZ) ; Loy; Douglas; (Chandler, AZ) ; Jiang;
Hanqing; (Chandler, AZ) |
Assignee: |
Arizona Board of Regents, a body
Corporate of the State of Arizona acting for and on the behalf of
A
Scottsdale
AZ
|
Family ID: |
41011823 |
Appl. No.: |
12/921896 |
Filed: |
April 6, 2009 |
PCT Filed: |
April 6, 2009 |
PCT NO: |
PCT/US2009/039577 |
371 Date: |
November 29, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61043223 |
Apr 8, 2008 |
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Current U.S.
Class: |
428/414 ;
156/327; 156/329; 156/330; 156/330.9; 156/331.7; 156/332; 156/335;
428/423.1; 428/426; 428/447; 428/457; 428/473.5; 428/480; 428/524;
428/702 |
Current CPC
Class: |
Y10T 428/31515 20150401;
H05K 3/386 20130101; Y10T 428/31551 20150401; Y10T 428/31663
20150401; H05K 3/007 20130101; Y10T 428/31678 20150401; H05K 1/0393
20130101; Y10T 428/31942 20150401; H05K 2201/0175 20130101; H05K
2203/0191 20130101; Y10T 428/31721 20150401; H01L 29/78603
20130101; H05K 2203/016 20130101; Y10T 428/31786 20150401 |
Class at
Publication: |
428/414 ;
156/327; 156/330.9; 156/332; 156/331.7; 156/330; 156/335; 156/329;
428/423.1; 428/447; 428/473.5; 428/480; 428/524; 428/426; 428/702;
428/457 |
International
Class: |
B32B 7/12 20060101
B32B007/12; C09J 179/08 20060101 C09J179/08; C09J 133/08 20060101
C09J133/08; C09J 175/04 20060101 C09J175/04; C09J 163/00 20060101
C09J163/00; C09J 161/06 20060101 C09J161/06; C09J 183/04 20060101
C09J183/04; B32B 27/00 20060101 B32B027/00; B32B 27/38 20060101
B32B027/38; B32B 27/40 20060101 B32B027/40; B32B 27/34 20060101
B32B027/34; B32B 27/30 20060101 B32B027/30; B32B 27/42 20060101
B32B027/42; B32B 17/10 20060101 B32B017/10; B32B 15/08 20060101
B32B015/08 |
Goverment Interests
STATEMENT OF GOVERNMENT FUNDING
[0002] This work was supported at least in part by U.S. Army
Research Labs (ARL) Grant No. W911NF-04-2-005. The U.S. Government
has certain rights in this invention.
Claims
1. A method for preparing a flexible substrate assembly comprising
attaching a flexible substrate to a rigid support with an adhesive
layer, wherein the adhesive layer comprises a viscoelastic polymer
having a glass transition temperature less than 180.degree. C. and
a decomposition temperature greater than 220.degree. C.
2. The method of claim 1, wherein the attaching comprises
depositing the adhesive layer on a surface of the rigid support;
and bonding the flexible substrate with the rigid support wherein
the adhesive layer is between the rigid support and flexible
substrate.
3. The method of claim 2, wherein the adhesive layer is deposited
by spin-coating, spray-coating, extrusion coating or preform
lamination.
4. The method of claim 1, wherein the adhesive layer has a
coefficient of thermal expansion ranging from about 10 to about
1000 ppm/.degree. C.
5. The method of claim 1, wherein the adhesive layer outgases at a
rate less than 2.times.10.sup.-4 Torr-liter/second.
6. The method of claim 4, wherein the adhesive layer comprises a
polyimide, polyacrylate, acrylic, urethane, epoxy, phenolic,
bis-maleimide, silicone, or siloxane.
7. The method of claim 6, wherein the adhesive layer comprises
n-butylacrylate, polysiloxane, polysilicone or polyimide.
8.-11. (canceled)
12. The method of claim 1, wherein the rigid support comprises a
semiconductor wafer, alumina, a glass, or a material CTE matched to
the flexible substrate.
13.-15. (canceled)
16. The method of claim 1, wherein the flexible substrate is a
plastic substrate or metal substrate.
17. The method of claim 16, wherein the flexible substrate is a
plastic substrate, and wherein the plastic substrate comprises
polyethylene naphthalate (PEN), polyethylene terephthalate (PET),
polyethersulfone (PES), polyimide, polycarbonate, cyclic olefin
copolymer, or mixtures thereof.
18. The method of claim 16, wherein the flexible substrate is a
metal substrate, and wherein the metal substrate comprises INVAR,
KOVAR, titanium, tantalum, molybdenum, aluchrome, aluminum,
stainless steel, or mixtures thereof.
19.-20. (canceled)
21. The method of claim 1, further comprising, prior to bonding of
the flexible substrate and the rigid carrier, forming an insulating
layer or metal layer directly on the adhesive layer; and placing a
double-sided adhesive tape directly on the insulating layer or
metal layer
22. The method of claim 21, wherein the method further comprises
forming an insulating layer directly on the adhesive layer and
placing a double-sided adhesive tape directly on the insulating
layer, and wherein the insulating layer comprises SiO.sub.2 or
SiN.
23. The method of claim 21, wherein the method further comprises
forming a metal layer directly on the adhesive layer and placing a
double-sided adhesive tape directly on the metal layer, and wherein
the metal layer comprises aluminum.
24. (canceled)
25. The method of claim 1, wherein the flexible substrate has a bow
or warp of less than about 100 m.
26. The method of claim 25, wherein the flexible substrate has a
bow or warp of less than about 60 m.
27. The method of claim 1, further comprising forming a display
architecture on the flexible substrate.
28. The method of claim 1, further comprising forming one or more
thin film transistors, organic light emitting diodes, inorganic
light emitting diodes, electrode arrays, field effect transistors,
passive structures and combinations thereof on a surface of the
flexible substrate.
29. An assembly comprising a flexible substrate, a rigid support,
and an adhesive layer, wherein the flexible substrate is attached
to the rigid support with the adhesive layer between the flexible
substrate and rigid support; and the adhesive layer comprises a
viscoelastic polymeric adhesive having a glass transition
temperature less than 180.degree. C. and a decomposition
temperature greater than 220.degree. C.
30. The assembly of claim 29, wherein the adhesive has a
coefficient of thermal expansion greater ranging from about 10 to
about 1000 ppm/.degree. C.
31. The assembly of claim 29, wherein the adhesive outgases at a
rate less than 2.times.10.sup.-4 Ton-liter/second.
32. The assembly of claim 30, wherein the adhesive layer comprises
a polyimide, polyacrylate, acrylic, urethane, epoxy, phenolic,
bis-maleimide, silicone, or siloxane.
33. The assembly of claim 32, wherein the adhesive layer comprises
n-butylacrylate, polysiloxane, polysilicone or polyimide.
34.-37. (canceled)
38. The assembly of claim 29, wherein the rigid support comprises a
semiconductor wafer, alumina, a glass, or a material CTE matched to
the flexible substrate.
39.-41. (canceled)
42. The assembly of claim 29, wherein flexible substrate is a
plastic substrate or metal substrate.
43. The assembly of claim 42, wherein the plastic substrate
comprises polyethylene naphthalate (PEN), polyethylene
terephthalate (PET), polyethersulfone (PES), polyimide,
polycarbonate, cyclic olefin copolymer or mixtures thereof.
44. The assembly of claim 42, wherein the metal substrate comprises
INVAR, KOVAR, titanium, tantalum, molybdenum, aluchrome, aluminum,
or stainless steel.
45. The assembly of claim 44, wherein the metal substrate comprises
stainless steel.
46. The assembly of claim 29, further comprising an insulating or
metal layer formed directly on the adhesive layer and a
double-sided adhesive tape directly on the insulating or metal
layer, wherein the flexible substrate is in contact with the
double-sided adhesive tape.
47. The assembly of claim 46, wherein the insulating layer
comprises SiO.sub.2 or SiN.
48. The assembly of claim 46, wherein the metal layer comprises
aluminum.
49. A method for flexible display processing comprising: producing
a flexible display; attaching the flexible display to a rigid
substrate according to claim 1, wherein the flexible substrate is
the flexible display.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 61/043,223 filed Apr. 8, 2008, incorporated by
reference herein in its entirety.
FIELD OF THE INVENTION
[0003] This invention generally relates to processing flexible
substrates and more specifically to a method for reducing warp and
bow of a flexible substrate during semiconductor processing.
BACKGROUND OF THE INVENTION
[0004] In the electronics industry, flexible substrates are quickly
becoming popular as a base for electronic circuits. Flexible
substrates can include a wide variety of materials including very
thin layers of metal, such as stainless steel, any of a myriad of
plastics, etc. Once a desired electronic component, circuit, or
circuits are formed on a surface of the flexible substrate, the
circuit can be attached to a final product or incorporated into a
further structure. Typical examples of such products or structures
are active matrices on flat panel displays, RFID tags on various
commercial products in retail stores, a variety of sensors,
etc.
[0005] One major problem that arises is stabilizing the flexible
substrate during processing. For example, in a process of
fabricating thin film transistors or thin film transistor circuits
on a substrate, a large number of process steps are performed
during which the substrate may be moved through several machines,
ovens, cleaning steps, etc. To move a flexible substrate through
such a process, the flexible substrate must be temporarily mounted
in some type of carrier or a rigid carrier must be removably
attached, so that the flexible carrier can be moved between process
steps.
[0006] However, the relatively high coefficient of thermal
expansion (CTE) for flexible substrates compared to inorganic
silicon or glass substrates leads to significant CTE induced strain
mismatch during temperature excursions including inorganic thin
film transistor (TFT) processing. This phenomenon introduces
significant bowing and warping and can lead to handling errors,
photolithographic alignment errors, and line/layer defects.
Therefore, there exists a need in the art to develop novel
compositions and methodologies for attaching a flexible substrate
to a rigid carrier to mediate the preceding limitations.
SUMMARY OF THE INVENTION
[0007] In a first aspect, the invention provides methods for
preparing a semiconductor assembly comprising attaching a flexible
substrate to a rigid support with an adhesive layer, wherein the
adhesive layer comprises a viscoelastic polymer having a glass
transition temperature less than 180.degree. C. and a decomposition
temperature greater than 220.degree. C.
[0008] In a second aspect, the invention provides assemblies
comprising a flexible substrate, a rigid support, and an adhesive
layer, wherein the flexible substrate is attached to the rigid
support with the adhesive layer between the flexible substrate and
rigid support; and the adhesive layer comprises a viscoelastic
polymer having a glass transition temperature less than 180.degree.
C. and a decomposition temperature greater than 220.degree. C.
[0009] In a third aspect, the invention provides methods for
flexible display processing comprising producing a flexible display
and attaching the flexible display to a rigid substrate according
to the first aspect of the invention, wherein the flexible
substrate is the flexible display.
DETAILED DESCRIPTION OF THE INVENTION
[0010] The term "bowing" as used herein means the curvature of a
substrate about a median plane. The term "warping" as used herein
means the linear displacement of the surface of a substrate with
respect to a line defined by the center of the substrate. For
example, if a substrate is uniformly bowed than the warp is about
twice the bow measurement.
[0011] The term "CTE matched material" as used herein means a
material which has a coefficient of thermal expansion (CTE) which
differs from the CTE of the referenced material by less than about
20%. Preferably, the CTEs differ by less than about 10%, 5%, 3%, or
1%.
[0012] The term "flexible substrate" as used herein means a
free-standing substrate comprising a flexible material which
readily adapts its shape. Preferably, the flexible substrate is a
preformed flexible plastic substrate or a preformed flexible metal
substrate. Preferred flexible metal substrates include FeNi alloys
(e.g., INVAR.TM., FeNi, or FeNi36; INVAR.TM. is an alloy of iron
(64%) and nickel (36%) (by weight) with some carbon and chromium),
FeNiCo alloys (e.g., KOVAR.TM., KOVAR.TM. is typically composed of
29% nickel, 17% cobalt, 0.2% silicon, 0.3% manganese, and 53.5%
iron (by weight), titanium, tantalum, molybdenum, aluchrome,
aluminum, and stainless steel. Preferred flexible plastic
substrates include polyethylene naphthalate (PEN), polyethylene
terephthalate (PET), polyethersulfone (PES), polyimide,
polycarbonate, and cyclic olefin copolymer. Such flexible
substrates are preferably thin; for example, about 1 .mu.m to 1 mm
thick. More preferably, a flexible substrate is about 50 .mu.m to
500 .mu.m; even more preferably, about 50 .mu.m to 250 .mu.m.
[0013] The term "viscoelastic adhesive" as used herein means an
adhesive which exhibits both viscous and elastic characteristics
when undergoing deformation. For example, a viscoelasctic material
resists shear flow and exhibits time dependent strain. Examples of
viscoelastic adhesive include, but are not limited to, polyimides,
polyacrylates, acrylics, urethanes, epoxies, phenolics,
bis-maleimides, silicones, and siloxanes.
[0014] The term "double-sided adhesive tape" as used herein means
any tape comprising a supporting backing with an adhesive material
on each of the two opposing faces thereof. The adhesives on
opposing faces can be the same or different, and include, for
example but not limited to elastomeric, thermoplastic,
thermosetting, pressure-sensitive, and/or light-curable adhesives
(e.g., visible or UV). Examples of double sided adhesives include,
but are not limited to, double sided powder coated silicone
adhesives (Argon PC500 family), or high performance silicone
adhesives (Adhesive Research Arcare 7876).
[0015] The term "stable" as used herein with respect to exposure of
a material to a particular temperature means that the referenced
material loses less than about 5% total weight by mass when
maintained at that temperature under a nitrogen or argon atmosphere
for a period of about 1 hour.
[0016] The present invention provides a method for preparing a
semiconductor assembly comprising attaching a flexible substrate to
a rigid support with an adhesive layer, wherein the adhesive layer
comprises a viscoelastic polymer having a glass transition
temperature less than 180.degree. C. and a decomposition
temperature greater than 220.degree. C. Generally, the viscoelastic
polymer comprises a polymer having a glass transition temperature
ranging from about 25 to 180.degree. C. Preferably, the glass
transition temperature ranges from about 50 to 180.degree. C., or
100 to 180.degree. C. Further, the viscoelastic polymers of the
present disclosure are stable under processing conditions exceeding
220.degree. C. Preferred viscoelastic polymers are stable at
temperatures ranging from about 220 to 400.degree. C. In certain
embodiments, the viscoelastic polymers are stable at temperatures
ranging from about 220 to 300.degree. C.
[0017] Further, the adhesive layer can have a coefficient of
thermal expansion (CTE) greater than about 10 ppm/.degree. C. In
general, the CTE of the adhesive can range from about 10 to 1000
ppm/.degree. C. In one embodiment, the adhesive layer may also
outgas at a rate less than about 2.times.10.sup.-4
Ton-liter/second. The adhesive layer outgassing can range from
about 1.times.10.sup.-10 to 2.times.10.sup.-4 Ton-liter/second.
[0018] In particular, the viscoelastic polymer can comprise
elastomeric, thermoplastic, or pseudothermoplastic saturated or
unsaturated hydrocarbon, siloxane, or silicone polymers.
Preferably, the viscoelastic polymer comprises acrylics, epoxies,
phenolics, urethanes polyimides, or siloxanes. More preferably, the
viscoelastic polymer comprises n-butylacrylate, polysiloxane,
polysilicone or polyimide. In one embodiment, the viscoelastic
polymer comprises n-butylacrylate. In one embodiment, the
viscoelastic polymer comprises polysiloxane. In one embodiment, the
viscoelastic polymer comprises polysilicone. In one embodiment, the
viscoelastic polymer comprises polyimide.
[0019] To prepare an assembly comprising a flexible substrate, a
rigid support, and an adhesive layer comprising the viscoelastic
polymer, the adhesive layer can be deposited onto the rigid carrier
or flexible substrate according to methods known to those skilled
in the art. The adhesive layer can be deposited on the rigid
carrier or flexible substrate using a solution of the adhesive
material, and can be prepared according to any method known to
those skilled in the art for preparing a layer from a solution. For
example, the solution can be spray coated, drop cast, spin coated,
webcoated, doctor bladed, or dip coated to produce an adhesive
layer on the rigid carrier or flexible substrate. Alternatively,
the adhesive layer can be extrusion coated or pre-form laminated
onto the rigid carrier or flexible substrate. Preferably, the
adhesive layer comprising the viscoelastic polymer is between about
1 .mu.m and 40 .mu.m thick, and more preferably between about 2
.mu.m and 20 .mu.m thick.
[0020] In certain embodiments, the layer can be formed on the rigid
carrier by spin coating a solution, i.e., by dispensing the
solution on a surface of the rigid carrier and spinning the carrier
to evenly distribute the solution. One skilled in the art will
understand that the thickness of the layer, produced by spin
coating, can be controlled by selection of the concentration of the
adhesive material in the solvent, the viscosity of the solution,
the spinning rate, and the spinning speed.
[0021] The solution layer can be dried, prior to bonding of the
flexible substrate or rigid carrier, to essentially remove any
remaining solvent. This drying can be according to any method known
to those skilled in the art provided the method does not cause
deterioration of the substrate, carrier, and/or adhesive material.
For example, the layer can be dried by heating the layer at a
temperature in the range of approximately 80.degree. C. to
180.degree. C., and preferably, about 100.degree. C. to 130.degree.
C. In another example, the layer can be dried by heating the layer
in a vacuum at a temperature in the range of approximately
100.degree. C. to 180.degree. C. In yet another example, the layer
can be dried by heating the layer at a temperature in the range of
approximately 80.degree. C. to 180.degree. C., followed by heating
the layer in a vacuum (e.g., less than about 1 Torr) at a
temperature in the range of approximately 100.degree. C. to
180.degree. C. In either heating process, the layer can be heated
for about 10 to 120 minutes until substantially all the solvent is
removed. One skilled in the art will recognize that higher
temperatures (e.g., up to 300.degree. C.) can be used in any of the
heating steps provided the adhesive material, flexible substrate,
and/or rigid carrier remains stable during heating.
[0022] Alternatively, to prepare an assembly comprising a flexible
substrate, a rigid support, and an adhesive layer, the adhesive
layer can be deposited onto the back side of flexible substrate,
followed by an optional drying and/or vacuum drying process, as
discussed previously. Preferably, when the adhesive layer is formed
on the flexible substrate, the layer is produced by spin coating of
a solution of the adhesive followed by drying of the layer, as
discussed previously.
[0023] The rigid carrier can comprise a semiconductor wafer,
alumina, a glass, or a material CTE matched to the flexible
substrate, as described herein. For example, the semiconductor
wafer can comprise Si, and, in particular, Si(100) or Si(111). In a
preferred embodiment, the rigid support comprises alumina. In
another embodiment, the rigid support comprises a material CTE
matched to the flexible substrate.
[0024] Typically, the flexible substrate can be a plastic substrate
or metal substrate. Preferred plastic substrates include, but are
not limited to, those substrates comprising polyethylene
naphthalate (PEN), polyethylene terephthalate (PET),
polyethersulfone (PES), polyimide, polycarbonate, cyclic olefin
copolymer or mixtures thereof. Preferred metal substrates include,
but are not limited to, those substrates comprising INVAR, KOVAR,
titanium, tantalum, molybdenum, aluchrome, aluminum, or stainless
steel. In certain embodiments, the flexible substrate comprises
stainless steel. For example, when a stainless steel substrate is
used according to the methods described herein, the rigid support
comprises alumina.
[0025] The flexible substrate can be bonded to the rigid support
with the adhesive layer in between, according to any methods known
to those skilled in the art. In one embodiment, bonding the
flexible substrate comprises heating the adhesive layer (either on
the flexible substrate or the rigid carrier, supra) to a softened
state, i.e., above the glass transition temperature (T.sub.g) of
the viscoelastic polymer, and contacting the flexible substrate
with to the adhesive-coated carrier. The specific softening
temperature for use in the present invention can be determined
empirically based on the teachings herein, and depends upon the
specific material used in adhesive layer. For example, T.sub.g can
be determined using techniques such as, but not limited to,
thermogravimetric analysis (TGA), thermomechanical analysis (TMA),
differential scanning calorimetry (DSC), and/or dynamic mechanical
analysis (DMA).
[0026] In one embodiment, the flexible substrate comprises
stainless steel, the rigid support comprises alumina, and the
adhesive layer comprises n-butylacrylate. In another embodiment,
the flexible substrate comprises stainless steel, the rigid support
comprises alumina, and the adhesive layer comprises polysiloxane.
In another embodiment, the flexible substrate comprises stainless
steel, the rigid support comprises alumina, and the adhesive layer
comprises polysilicone. In another embodiment, the flexible
substrate comprises stainless steel, the rigid support comprises
alumina, and the adhesive layer comprises polyimide.
[0027] In further embodiments, the adhesive layer may comprise more
than one constituent layer. For example, the adhesive layer can
comprise a first layer comprising a viscoelastic polymer and a
second layer formed over the viscoelastic polymer. For example, the
second layer can comprise a metal or insulating material layer.
Preferred metals include, but are not limited to, metals which can
be deposited by sputtering, for example, aluminum, gold, and
silver. Preferred insulating layers include those which can be
deposited by plasma enhanced chemical vapor deposition (PECVD),
such as SiN and SiO.sub.2. Such metal films typically can have a
thickness ranging from about 50 .ANG. to about 10,000 .ANG.. In
certain embodiments, the thickness can range from about 100 .ANG.
to about 5000 .ANG., or about 500 .ANG. to about 5000 .ANG., or
about 1000 .ANG. to about 5000 .ANG..
[0028] In yet further embodiments, the adhesive layer may comprise
three or more constituent layers. For example, the adhesive layer
can comprise a first layer comprising a viscoelastic polymer, as
discussed previously, a second layer formed over the viscoelastic
polymer, such as a metal or insulating layer, and a third layer
formed over the metal film. In certain embodiments, the third layer
can comprise a double-sided adhesive tape. Preferred metals
include, but are not limited to, metals which can be deposited by
sputtering, for example, aluminum, gold, and silver. Preferred
insulating layers include those which can be deposited by plasma
enhanced chemical vapor deposition (PECVD), such as, SiN and
SiO.sub.2. Such metal films typically can have a thickness ranging
from about 50 .ANG. to about 10,000 .ANG.. In certain embodiments,
the thickness can range from about 100 .ANG. to about 5000 .ANG.,
or about 500 .ANG. to about 5000 .ANG., or about 1000 .ANG. to
about 5000 .ANG..
[0029] In another embodiment, bonding the flexible substrate can
comprise depositing a layer of a metal or insulating layer directly
on the adhesive layer; positioning a double-sided adhesive directly
on the metal or insulating layer; and positioning the substrate
directly on the double-sided adhesive. Preferred metals include,
but are not limited to, metals which can be deposited by
sputtering, for example, aluminum, gold, and silver. Preferred
insulating layers include those which can be deposited by plasma
enhanced chemical vapor deposition (PECVD), such as, SiN and
SiO.sub.2. Preferred double sided adhesives include, but are not
limited to, double sided powder coated silicone adhesives (Argon
PC500 family), or high performance silicone adhesives (Adhesive
Research Arcare 7876) or similar.
[0030] After bonding of the flexible substrate to the rigid
support, one or more of any of a number of electronic can be
constructed on a surface of the flexible substrate. For example,
one or more thin film transistors, organic and/or inorganic light
emitting diodes, electrode arrays, field effect transistors,
passive structures, and combinations thereof. In other examples, a
display architecture can be formed on the flexible substrate
attached to a rigid carrier according to the methods described
herein.
[0031] It has been unexpectedly been found that such viscoelastic
polymers serve to mediate stresses and/or strains introduced into a
flexible substrate due to a CTE mismatch between the overlying
flexible substrate and the underlying rigid support. Notably, the
viscoelastic polymers utilized herein minimize warping and/or
bowing of the flexible substrate as a result of the thermal
stresses and/or strains introduced during, for example,
semiconductor manufacturing processes.
[0032] For example, the bowing and/or warping of a flexible
substrate, when attached to a rigid support according to any of the
preceding methods and embodiments, can be less than about 100
.mu.m; preferably, the bowing and/or warping of a flexible
substrate, when attached to a rigid support according to any of the
preceding methods is less than about 75 .mu.m; even more
preferably, the bowing and/or warping of a flexible substrate, when
attached to a rigid support according to any of the preceding
methods is less than about 60 .mu.m.
EXAMPLES
[0033] A variety of exemplary carriers were bonded to one of 2
exemplary flexible substrates (PEN or stainless steel (SS)) of
thickness as recited in Table 1, using exemplary pressure
sensitive, adhesives, which include acrylates, polyacrylates, and
silicones. The adhesives include spin-on adhesives and adhesive
tapes.
[0034] The resulting bow and flex data are provided in Table 1.
This and similar data reveal that the smaller the CTE delta
(difference) between carrier and flex material, the smaller the
bow. Furthermore, the data demonstrate that viscoelastic adhesives
reduce the amount of bow within a carrier/flex material system. For
example, looking at the silicon/SS systems, ArClad (available from,
for example, Adhesives Research, Glen Rocks, Pa.) has greater
viscoelasticity than DCPC500 (available from, for example, ESD
Tapes, Monrovia, Calif.), and yields less bow.
TABLE-US-00001 TABLE 1 Bow and Warp of Exemplary
Carrier/Substrate/Flex material Carrier FS Carrier CTE Adhesive
Flex sub. thick. (um) FS CTE Bow Warp Alumina 7.6 FX930 PEN 200
20-25 82.86 113.66 Silicon 3.5 DCPC5000 PEN 125 20-25 137.71 160.9
Silicon 3.5 FX930 PEN 125 20-25 159.4 180.93 Silicon 3.5 DCPC500 SS
100 9-12 >400 >600 Silicon 3.5 ARClad SS 100 9-12 >150
>200 Carrier CTE Adhesive FS FS Th (um) CTE Bow Warp Alumina 7.6
FX930 PEN 200 20-25 82.86 113.66 Silicon 3.5 DCPC5000 PEN 125 20-25
137.71 160.9 Silicon 3.5 FX930 PEN 125 20-25 159.4 180.93 Silicon
3.5 DCPC500 SS 100 9-12 >400 >600 Silicon 3.5 ARClad SS 100
9-12 >150 >200
* * * * *